Airport connections

Author: Partho Biswas

README.md

@@ -860,6 +860,7 @@ BTW, it's a great interview prep tool. You will never go wrong with this and you
 |05| [Breadth_First_Search](algoexpert.io/questions/Breadth-first_Search.md) | [Python](algoexpert.io/python/Breadth_First_Search.py)|
 |06| [Boggle_Board](algoexpert.io/questions/Boggle_Board.md) | [Python](algoexpert.io/python/Boggle_Board.py) |
 |07| [Rectangle_Mania](algoexpert.io/questions/Rectangle_Mania.md) | [Python](algoexpert.io/python/Rectangle_Mania.py) |
+|07| [Airport_Connections](algoexpert.io/questions/Airport_Connections.md) | [Python](algoexpert.io/python/Airport_Connections.py) |
 
 </p>
 </details>

algoexpert.io/python/Airport_Connections.py

@@ -0,0 +1,79 @@
+def airportConnections(airports, routes, startingAirport):
+    airportGraph = createAirportGraph(airports, routes)
+    unreachableAirportNodes = getUnreachableAirportNodes(airportGraph, airports, startingAirport)
+    markUnreachableConnections(airportGraph, unreachableAirportNodes)
+    return getMinNumberOfNewConnections(airportGraph, unreachableAirportNodes)
+
+
+def createAirportGraph(airports, routes):
+    graph = {}
+    for airport in airports:
+        graph[airport] = AirportNode(airport)
+    for route in routes:
+        airport, connection = route
+        graph[airport].connections.append(connection)
+    return graph
+
+
+def getUnreachableAirportNodes(airportGraph, airports, startingAirport):
+    visitedAirports = {}
+    dfsFromStartingAirport(airportGraph, startingAirport, visitedAirports)
+
+    unreachableAirportNodes = []
+    for airport in airports:
+        if airport in visitedAirports:
+            continue
+        airportNode = airportGraph[airport]
+        airportNode.isRechable = False
+        unreachableAirportNodes.append(airportNode)
+    return unreachableAirportNodes
+
+
+def dfsFromStartingAirport(airportGraph, startingAirport, visitedAirports):
+    if startingAirport in visitedAirports:
+        return
+    visitedAirports[startingAirport] = True
+    connections = airportGraph[startingAirport].connections
+    for connection in connections:
+        dfsFromStartingAirport(airportGraph, connection, visitedAirports)
+
+
+def markUnreachableConnections(airportGraph, unreachableAirportNodes):
+    for airportNode in unreachableAirportNodes:
+        airport = airportNode.airport
+        unreachableCOnnections = []
+        dfsAddUnreachableConnections(airportGraph, airport, unreachableCOnnections, {})
+        airportNode.unreachableConnections = unreachableCOnnections
+
+
+def dfsAddUnreachableConnections(airportGraph, airport, unreachableCOnnections, visitedAirports):
+    if airportGraph[airport].isRechable:
+        return
+    if airport in visitedAirports:
+        return
+    visitedAirports[airport] = True
+    unreachableCOnnections.append(airport)
+    connections = airportGraph[airport].connections
+    for connection in connections:
+        dfsAddUnreachableConnections(airportGraph, connection, unreachableCOnnections, visitedAirports)
+
+
+def getMinNumberOfNewConnections(airportGraph, unreachableAirportNodes):
+    unreachableAirportNodes.sort(key=lambda airport: len(airport.unreachableConnections), reverse=True)
+
+    numberOfNewConnections = 0
+    for airportNode in unreachableAirportNodes:
+        if airportNode.isRechable:
+            continue
+        numberOfNewConnections += 1
+        for connection in airportNode.unreachableConnections:
+            airportGraph[connection].isRechable = True
+    return numberOfNewConnections
+
+
+class AirportNode:
+    def __init__(self, airport):
+        self.airport = airport
+        self.connections = []
+        self.isRechable = True
+        self.unreachableConnections = []

algoexpert.io/questions/Airport_Connections.md

@@ -1,65 +1,17 @@
-## Airport Connections
+## Airport_Connections
 
 #### Problem Statement
 
-You are given a list of airports (three-letter codes like 'JFK'), a list of routes (one-way ights from one airport to another like ['JFK', 'SFO']), and
-a starting airport. Write a function that returns the minimum number of airport connections (one-way ights) that need to be added in order
-for someone to be able to reach any airport in the list, starting at the starting airport. Note that the connections don't have to be direct; it's
-okay if an airport can only be reached from the starting airport by stopping at other airports rst.
 
-Sample input:
-[
-"BGI",
-"CDG",
-"DEL",
-"DOH",
-"DSM",
-"EWR",
-"EYW",
-"HND",
-"ICN",
-"JFK",
-"LGA",
-"LHR",
-"ORD",
-"SAN",
-"SFO",
-"SIN",
-"TLV",
-"BUD",
-],
-[
-["DSM","ORD"],
-["ORD","BGI"],
-["BGI","LGA"],
-["SIN","CDG"],
-["CDG","SIN"],
-["CDG","BUD"],
-["DEL","DOH"],
-["DEL","CDG"],
-["TLV","DEL"],
-["EWR","HND"],
-["HND","ICN"],
-["HND","JFK"]
-["ICN","JFK"],
-["JFK","LGA"],
-["EYW","LHR"],
-["LHR","SFO"],
-["SFO","SAN"],
-["SFO","DSM"],
-["SAN","EYW"],
-],
-"LGA"
+![alt text](Airport_Connections_1.png "Airport_Connections")
+![alt text](Airport_Connections_2.png "Airport_Connections")
 
-Sample output: 3
 
 
 #### Explanation
 
-We can use a Stack here
 
 
 #### Solution
 
 Check this [Python](../python/Airport_Connections.py) code.
-